Deaerated stock flow control



Sept- 21, 1965 R. G. KAISER ETAL DEAERATED STOCK FLOW CONTROL 2Sheets-Sheet l Filed Oct. 4, 1961 2 Sheets-Sheet 2 R. G. KAISER ETALDEAERATED STOCK FLOW CONTROL Sept. 21, 1965 Filed Oct. 4, 1961 UnitedStates Patent O 3,206,917 DEAERATEI) STCK FLW CQNTROL Robert G. Kaiser,Ho-Ho-Kus, NJ., and .iohn C. Stewart,

North Tarrytown, NSY., assignors to Clark 8: Vicario Corporation, NorthTarrytown, NSY., a corporation of New York Filed Oct. 4, 1961, Ser. No.142,987 10 Ciaims. (Cl. 55-41) This invention relates to papermaking,and concerns apparatus and method for :assuring a substantially constantflow of deaerated papermaking stock, which may also be de-dirted, `froma deaerating station.

`In current papermaking practice, an aqueous suspension of cellulosicpapermaking stock is fed to the headbox f a papermaking machine, whencethe stock is supplied to the wire of the machine. It is important thatthe ilow of stock to the headbox be carefully regulated .andsubstantially uniform, else the weight and caliper of the paper made bythe machine is subject to unacceptable variation. Particularly with theadvent of increasingly rapid machine speeds, the necessity for moreaccurate control assuring constant flow of stock to the headbox hasbecome of commensurately greater importance.

More modern methods of paper-making take advantage of the discovery thata superior product is obtained by deaeratiug the aqueous cellulosicsuspension of stock before it reaches the machine. Method and apparatusfor accomplishing such deaeration .are disclosed in U.S. Patents2,614,656, 2,642,950 and 2,685,937, and briey entail atomizing `a stocksuspension into an enclosed tank or receiver which is maintained undersignificantly reduced pressure, well below atmospheric and preferablyabout 0.3 inch .of mercury above the boiling point of the stock withinthe receiver. The stock is advantageously de-dirted as well asdeaerated, .as by the method and apparatus shown in U.S. Patents2,717,536, 2,876,860 and 2,931,503.

in the environment of a stock deaerating station, previously knownmanners of regulating the oW of stock to the papermaking machine workless effectively, if at all. The significantly reduced pressure with thereceiver seriously interferes with adequate regulation. For exampie,valvinlg in the discharge pipe connecting receiver and headbox may beconnected with displacement iioats or the like Within the receiver in an.attempt to maintain a constant level of stock in the receiver, but itis found that such control valves tend to be in substantially constantmotion, and .the system tends continually to .overcor'rect and tounder-correct, causing significant variation in dow.

What has up to now been regarded as constant feed has thus actually beena fluctuating feed, but the fluctuations have bee-n tolerated.Technological advancement has created a need for more refined regulationand a more carefully controlled flow. The necessity for c-onveyingdeaerated stock to the machine under vacuum has made the problem moreacute.

The present invention provides a solution to this problem and assures asubstantially constant flow of papermaking stock from a deaeratedstation operating under substantially less than atmospheric pressure. Afeature xof the invention is maintenance of a substantially constantlevel of stock in the receiver for supply to the headbox. Correlatedimprovements and advantages include means for rejecting foam, scum, andother undesirable fractions residing on the surface of the stock in `thereceiver.

A particularly important advantage of the present invention is that itpermits simple and rapid changeover by the paperm-aker from a givengrade `or weight of paper to one of a different grade. Such changeoversmay inice volve altering significantly the volume of stock fed to theheadbox; presently known control systems must be manually andempirically adjusted to compensate for such substantial changes in iiow,but the method and apparatus of the present invention rapidly and.automatically accommodate changes in volume of the magnitude referredto. In addition, during start-up of the paper machine the transientperiod of level instability is greatly reduced and a stable operatinglevel in the receiver is achieved in the shortest possible time. Theresultant saving in time alone is of appreciable economic importance.

Other advantages and features of the invention will in part be obviousand will in part appear hereinafter.

In accordance with the present invention, an enclosed stock receiver ina deaerating station is equipped with evacua-ting means, suitably avacuum pump, to maintain the receiver under substantially less thanatmospheric pressure. The receiver cooperates with means admitting feedstock thereto as .an atomized spray and is adapted to collect theresultant deaerated stock ina pond within said receiver. Means areprovided to withdraw product deaerated stock from the pond within thereceiver. Weir means are provided Withinthe receiver and .are positionedwith the upper terminus 4of the Weir at or slightly below the desiredlevel of the pond of product deaerated stock within the receiver in suchmanner that excess product stock above the desired pond level overflowsthe Weir.

A closed chamber having a capacity substantially less than that of thereceiver communicates with the receiver a-nd is adapted t-o receive andpool stock overflowing the weir for recycling. Recycle stock returnmeans are provided to convey the recycle stock from the pool in theclosed chamber to the receiver. At least a slight excess of feed stockis supplied to the receiver over that which is withdrawn as productdeaerated stock, resulting in continual overflow of excess stock to thechamber for recycling. Means are provided to regulate the rate of flowof the recycle stock from the chamber to the receiver responsively tothe level of the recycle stock pool in the chamber, suitably byemployment of recycle stock pool level sensing means operativelyconnected lto valve means located in the recycle stock return meansconveying the recycle stock to the receiver. ln this manner the level ofthe recycle stock pool is held substantially constant at a predeterminedlevel or within predetermined lim-its.

It is desirable that the total volume of feed stock to the receiver(fresh stock plus recycle stock) not be subject to wide variation and itis accordingly preferred that an increase in the volume of recycle stockbe accompanied by a decrease in the amount of fresh stock supplied, andconversely. This may be accomplished in accordance with the invention bysupplying recycle stock to the intake side of the feed pump at a pointahead of the fresh stock intake.

Variations in flow of product deaerated stock from the receiver areprincipally due to an inconstant level of product stock forming the pondin the receiver, either through inadequate regulation or through huntingor other iiuctuation as control devices measure the pond level and seekto restore or maintain the proper level by continually compensating forchanges. The present invention maintains the level of the pond of stocksubstantially constant at or slightly above the predetermined height ofthe upper terminus of the Weir, and avoids pond level sensing devicesand associated control equipment and consequently avoids such seeking.Under equilibrium conditions the rate of excess stock overflowing theWeir is constant, as is the level of recycle stock in the chamber.Imbalance in the system (e.g., when the discharge rate is altered) israpidly and automatically corrected either by an increase or decrease inthe recycle rate, and the variationin pond level within the receiver ismerely the vvariation in head overflowing the weir, at most an inch orso. Thus, the volume of overow stock, while small in relation to thehigh capacity receiver, is large in relation to the small capacitychamber and causes a correspondingly significant in recycle stock poollevel. The effect of change of pond level within the receiver is thusmagnified in the pooled recycle stock level within the chamber, andcorrection is rapidly and automatically made by responsive alteration ofthe recycle rate. Thus the magnitude of any permitted variation in flowrate from the receiver pond is extremely small, and the variation itselfis promptly eliminated.

While the degree of refinement of control and sensing devices is subjectto variance and may readily be selected by one skilled in the art=tomeet a given set of circumstances, it is an advantage of the presentinvention that less rened and consequently less expensive controldevices may be employed herein. Any fluctuation in level occurs in theoverliow chamber pool and does not have any significant effect on therate of flow of product stock from the receiver. Such uctuations orhunting of the chamber pool level is not disadvantageous; the level ofstock in the receiver, which is important, does not changesignificantly.

The invention may readily be apprehended by reference to theaccompanying drawing in which FIG. 1 is a schematic representation of acontrol system in accordance With the invention, FIGS. 2, 3 and 4 showequivalent arrangements of the weir means within receiver, and FIGS. 5and 6 illustrate a preferred nozzle for introducing stock into thereceiver. FIGURE 7 is a schematic representation of an alternativearrangement of a control system similar to that shown in FIGURE l.

Referring now particularly to FIG. 1, a stock deaerating station 16 isprovided with an enclosed receiver 1 connected through port 2 tosuitable vacuum-inducing means for maintaining the interior of thereceiver under substantially less than atmospheric pressure. Pump 4draws dilution white water from wire pit or silo 3 and new thick stockfrom stock preparation chest or other source 42 in desired proportion byappropriate adjustment of values or other means of regulation (notshown) in accordance with known practice. The resulting mixture ispumped through conduit 30 to header 43 for introduction to receiver 1.

Feed stock is atomized into receiver 1 from header 43 by appropriatenozzles, suitably of the type shown in FIGS. 5 and 6. In FIG. 1 areshown hydrocyclones 5, which de-dirt the feed stock and atomize it intoreceiver 1 through inlet pipes 31. The nozzle of FIG. 5 may besubstituted for `hydrocyclones 5, or the stock may be directly admittedto the receiver through inlet pipes 31, so long as the feed stock isatomizingly admitted. Deaerating conditions are enhanced by the use ofnozzles or hydrocyclones. A pond or reservoir 19 of deaerated stock iscollected in receiver 1. Inlet pipes 31 extend upwardly through pond 19and admit atomized feed stock above the level 8 of pond 19.

Product stock is withdrawn from receiver 1 through port 10, located ator near the bottom of receiver 1, by conduit 11 and pump 12 is fedthrough conduit 25 to headbox 13 and thence to the wire 14 of apapermaking machine. Papermakers valve 26 is located in conduit andpermits regulation of the rate of ow of stock by the papermakeraccording to the demand for the particular weight of paper being made.

At least a slightly greater amount of stock is fed to Y the receiverthrough header 43 and inlet pipes 31 than is withdrawn through port 10.Conveniently, the feed may be slightly greater than the maximum demandof the papermaking machine. Valve 29 in conduit 30 may be employed toregulate the flow of feed stock to the appropriate or desired volume. f

There is provided within receiver 1 a weir 6, the Weir being sopositioned as to permit excess stock to overflow its upper terminus 9for recycling. Recycle stock overflowing the Weir passes to chamber 7,which is adapted to receive and pool overflow stock. Recycle stock fromchamber 7 is returned at a controlled rate to receiver 1, as hereinaftermore fully appears. In FIG. 1, chamber 7 is shown communicating by meansof a conduit 60 to the intake side of pump 15. Alternatively, ifdesired, chamber 7 may communicate by a barometric drop leg to theintake side of pump 4 for regulated return of overiiow stock to thereceiver, as shown in FIG. 7.

In FIG. 1,recycle stock is returned to receiver 1 from chamber 7 by pump15 and conduit 20. Valve 21 in conduit 20 is operatively connected withsensing means 17, which senses and is responsive to the level of thepool of recycle stock in chamber 7, so that the flow of recycle stockfrom chamber 7 is controlled responsively to the level of the poolwithin the chamber. Sensing means 17 may be any of a variety of devices,illustratively a iioat, differential pressure cell, or the like. Thesensing means 17 may conveniently operate through control instrument 18by pneumatic or electrical means 44 and 45 to regulate valve 21responsively to changes in the level of the pool recycle stock withinchamber 7 to maintain that level substantially constant or withinpredetermined limits.

In a preferred embodiment of the invention recycle stock is conveyedfrom chamber 7 through conduit 20 to the intake side of feed-pump 4,which supplies stock to receiver 1. Particularly when the recycle stockis introduced at a point ahead of the fresh stock, as shown in FIG. l, alesser variation in volume of feed stock supplied to the receiver isobtained. Under this arrangement, f

all recycle stock is fed back to the receiver and the required amount offresh stock is drawn as needed. Fluctuations caused by movement of valve21 are thus compensated by the flow of fresh stock into the system; theow of product stock from the receiver is unaffected. Equivalentarrangements to that illustrated will be apparent to those skilled inthe art. Since the recycle stock has been deaerated, greater efficiencyis obtained by assuring its return to the receiver.

FIG. 4 shows an alternative embodiment of an overiiow Weir of the typeshown in FIG. 1. According to this embodiment a weir 6 having an upperterminus 9 is provided as before, with the addition of a baiiie plate 22extending downwardly from a point above weir 6, said baffle plate 22terminating below the level 8 of the stock in the receiver 1. The stockin receiver 1 which overflows the top 9 of Weir 6 is'thus drawn from apoint below the surface 8 of the stock. In this manner scum and otherundesirable surface matter not drawn off to chamber 7, and possibleinterference with the operation of pump 15 and other pumps which may beemployed in the system is thereby avoided. A venting aperture (notshown) is provided in baflie 22 and located at a point well above level8 of the stock in receiver 1 to equalize pressure on either side of thebafiie. Baffle 22 serves also to prevent stock spray 24 emitted frominlet pipe 31 from being diverted into chamber 7 and is particularlyuseful where a plurality of inlets are provided to admit stock toreceiver 1.

A preferred nozzle for use in conjunction with inlet pipes 31 forintroducing the feed stock to receiver'l as a spray is shown in FIGS. 5and 6 and comprises a hollow truncated cone 50 having a solid base 51and an open top 52 adapted to fit inlet pipe 31. Supply pipe 53, adaptedto convey feed stock to the nozzle from header 43, is fitted to cone 50so that entering stock will be admitted under pressure tangentially. Inoperating a swirling action ensues within cone 50k and the feed stockcyclonically rises through the nozzle and feed pipe 31 and atomizinglyenters the receiver.

In operation of the disclosed system, white water from pit 3 and thickstock from chest 42 are fed, along with recycle stock from conduit 2G,through pump 4, conduit 30, header 43 and inlet pipes 31 intoreceiver 1. Concurrently, stock is withdrawn from receiver 1 throughport and conduit 11 by the action of pump 12 and is sent to headbox 13of the papermaking machine. By reason of the relatively greater iiow ofstock into the receiver, a certain amount of stock overflows the upperterminus 9 of weir 6 within receiver 1 into a pool in chamber 7, whenceit is forced by pump 15 and pump 4 back into receiver 1. The amount ofstock so recycled is regulated by valve 21 in conduit 20 on the eiuentside of pump 15, valve 21 being operatively controlled responsively tosensor 17, which measures the level of the recycle stock pool in chamber7. Under equilibrium conditions the amount of stock overflowing weir 6is constant and equal to the amount of stock drawn from chamber 7. Valve21 maintains a constant aperture or opens and closes slightly.

Assuming that the papermaker desires to increase the consistency of thefurnish to the headbox, he will manually or otherwise partially closepapermakers valve 26. As a result less stock is drawn from receiver 1through port 10 and an imbalance in liow rates results. An in creasedamount of stock overilows the upper terminus 9 of weir 6 into chamber 7,and the consequent rise in the level of the recycle stock pool inchamber 7 is detected by sensor 17. Valve 21 in conduit 20 in the efuentside of pump 15 opens responsively to the rise of the recycle stock poollevel in chamber 7, permitting recycle stock to ilow from the chamber ata greater rate. The recycle stock is fed back to receiver 1 through pump4, a lesser amount of white water being drawn from wire pit 3. Shouldcontrol 18 have overcompensated so that the level of the pool in chamber7 falls below a predetermined level, valve 21 will be responsivelyclosed partially. In this manner the level of the recycle stock pool inleg 7 is held at a predetermined point or within predetermined limits.

If, conversely, the papermaker should desire to decrease the consistencyof the furnish to the headbox and thus open valve 26, a greater amountof stock is drawn from receiver 1 through port 10 with the result thatthe amount of stock overflowing the upper terminus 9 of Weir 6decreases. The level of stock in chamber 7 falls and valve 21 in conduit20 responsively closes. Less recycle stock is thus supplied to pump 4and a greater volume of white water is consequently drawn from wire pit3. As the volume of stock overowing the weir increases, the level of thepool in chamber 7 rises and valve 21 responsively opens partially,causing equilibrium to be restored.

While some over-compensation or under-compensation may occur in theresponsive operation of valve 21, the level of recycle stock in chamber7 is aected but the level of stock in receiver 1 is not significantlychanged. By virtue of the relatively small capacity of the chamber ascompared with the receiver, a major increase or decrease of recyclestock level in the chamber corresponds to a change of but a very smallfraction of an inch in the level of stock in the receiver. Verysensitive control of stock level may therefore be achieved by thepractice of invention.

From the foregoing discussion it will be seen that the present inventionserves to maintain a constant level of stock in receiver 1 when thesystem is in equilibrium, and it further causes the system repaidly tobe restored to equilibrium when such equilibrium is disrupted as by achange in setting of papermakers valve 26. Achieving a new balance ofilow to the papermaking machine requires a discrete amount of time,during which no useful production can be achieved. It is consequently ofgreat importance that the system of the present invention rapidlyrestores the system to equilibrium.

In one embodiment of the invention, which is to be taken as illustrativeand not in a limiting sense, receiver 1 has a diameter of 6 feet and alength of 14 feet and a pond capacity of 3500 gallons. The upperterminus 9 0f weir 6 is located approximately 3 inches below the centerline of the receiver. The maximum liquid level over the top of the weiris approximately 6 inches, and the minimum approximately 1 inch, withthe normal liquid level approximately 3 inches above the top of theWeir. The pool capacity of the chamber 7 is about 250 gallons. Theaverage ilow of stock over the weir into chamber 7 is approximately10-15% of the total flow and the balance of ow through port 10 to pump12 is about 85-90% of the total flow.

ln FIGS. 2 and 3 are shown equivalent arrangements of weir means withinthe receiver. In FIG. 2 the weir is probe-shaped and its upper surface 9may have a channel or may be provided with slots or holes through whichrecycle stock flows to chamber 7. Sensor 17 is provided to sense thelevel of the pool of recycle stock in chamber 7. ln FIG. 3 chamber 7 islocated within receiver 1 and the weir 6 is provided with aperturescommunicating with the chamber to permit accesses of recycle stockthereto. Sensor 17 is indicated as mounted on the outside wall of thereceiver but communicating with chamber 7 to sense the level of the poolof recycle stock therein.

An optional arrangement is shown in FIG. l whereby a conduit 2S shunts aportion of the product deaerated stock from conduit 25 to the intakeside of pump 4, the amount so diverted being regulated by valve 27.Stock so delivered is recycled to receiver 1 and the use of a portion ofthe product stock for recycle decreases the amount of the recycle stockoverflowing weir 6 and passing through pump 15. This arrangement takespart of the load orT pump 15 and permits use of a less expensive, lowercapacity pump in the 15 position.

We claim:

1. A method of treating papermaking stock suspension, which comprisesadmitting an air-containing aqueous suspension of papermaking stock asan atomized spray to an evacuated space within an enclosed stockreceiver maintained under a vacuum sutlicient to deaerate stock sprayedthereinto, collecting stock suspension thereby deaerated as a pond inthe receiver, withdrawing, deaerated stock suspension from the pond at alesser rate than the rate at which the aqueous stock suspension isadmitted to the receiver, conveying the deaerated stock suspensionwithdrawn from the pond to a point of use, maintaining the pond ofcollected deaerated stock suspension at a constant level by weir meansdening the maximum height of the pond, and recycling suspensionoverowing the Weir to the pond in the receiver.

2. A method for providing a constant flow of deaerated aqueouspapermaking stock from a stock deaerating station, which comprisesmaintaining an enclosed stock receiver under a vacuum suicient todeaerate papermaking stock subsequently sprayed thereinto, pumping amixture of fresh air-containing aqueous papermaking stock and a recyclestock to the receiver and spraying said stock mixture into the upperportion of the receiver, collecting the stock sprayed into the receiveras a pond within the lower portion of the receiver, withdrawingcollected stock from the pond at a lesser rate than the rate at whichstock is sprayed into the receiver and conveying the withdrawn collectedstock to a point of use, admitting stock from the pond overllowing aweir within the receiver to a chamber also maintained under vacuumsuicient to deaerate papermaking stock, withdrawing overowed stock fromthe chamber and returning the Withdrawn overlowed stock to the receiveras the recycle stock and mixing the withdrawn overowed stock with freshair-containing aqueous papermaking stock to provide the mixture beingpumped to the receiver.

3. Apparatus for providing a constant ow of deaerated aqueouspapermaking stock to a point of use, comprising an enclosed stockreceiver adapted to collect deaerated papermaking stock as a pondtherein and provide a space above the pond, evacuating means incommunication with the space above the pond in said receiver formaintaining the receiver under a vacuum suiiicient to deaeratepapermaking stock subsequently sprayed there into, means for sprayingair-containing aqueous papermaking stock into the evacuated space insaid receiver, means for withdrawing deaerated stock collected as a pondin said receiver and for conveying the withdrawn stock to said point ofuse, means communicating with the receiver for withdrawing stock fromthe pond including weir means maintained under a vacuum suiTicient todeaerate paper making stock by said evacuating means defining themaximum height of the pond of collected stock, and means for returningstock overflowing said Weir means to the pond of deaerated stockcollected in said receiver.

4. Apparatus according to claim 3 wherein the means for returning stockoveriiowing said weir Ameans to the pond of deaerated stock collected insaid receiver includes pump means, a barometric drop leg connecting saidreceiver to the input side of said pump means and adapted to conveystock overflowing said Weir means to said pump means, and conduit meansconnecting the output side of said pump means to said means for sprayingair-containing aqueous papermaking stock into the evacuated space insaid receiver.

5. Apparatus according to claim 3 wherein the means for returning stockoverowing said Weir means to the pond of deaerated stock collected insaid receiver includes rst pump means, iirst conduit means connectingsaid receiver to the intake side of said first pump means and adapted toconvey stock overflowing said weir means to said iirst pump means,second pump means, second conduit means connecting the output side ofsaid rst pump means to the input side of said second pump means, andthird conduit means connecting the output side of said second pump meansto said spraying means.

6. Apparatus according to claim 3 including bathe means cooperating withsaid Weir means to prevent surface stock, foam and spray fromoveriiowing said weir means.

7. Apparatus for providing a constant flow of deaer ated papermakingstock from a stock deaerating station, comprising an enclosed stockreceiver, evacuating means in communication with the upper interiorportion of said receiver lfor maintaining said receiver under a vacuumsuiiicienty to deaerate papermaking stock sprayed thereinto, means forspraying papermaking stock into the upper portion of said receiver,compartment means in the lower portion of said receiver adapted tocollect as a pond stock sprayed into the upper portion of said receiver,means for withdrawing stock from the pond thereof collected in saidcompartment means and for conveying stock so Withdrawn to a point ofuse, a chamber closed to the atmosphere and maintained under vacuumsuiiicient to deaerate papermaking stock by said evacuating means, meansdeiining a flow way between the receiver compartment means and thechamber including Weir means permitting overiiow `of stock from the pondto the chamber, and means for returning overiiowed stock from thechamber to the receiver compartment means.

8. Apparatus according to claim 7 including baiiie means cooperatingwith said weir means to prevent surface stock, foam and spray fromoverflowing said weir means.

9. Apparatus for providing a constant flow of deaerated aqueouspapermaking stock from a stock deaerating station, comprising anenclosed stock receiveradapted to collect deaerated stock as a pondtherein, evacuating means in communication with said receiver formaintaining the receiver under a vacuum suiiicient to deaeratepapermaking stock subsequently sprayed thereinto, means for sprayingair-containing aqueous papermaking stock into said receiver above thepond of deaerated stock collected therein and cooperating stock-feedingpump means and associated conduit means for conveying air-containingaqueous papermaking stock to said spraying means, a discharge conduitfrom said receiver for withdrawing and conveying to a point of usedeaerated stock from the pond thereof collected in said receiver, weirmeans `in said receiver having an upper terminus slightly below thedesired level of the pond of collected deaerated stock, a chamber closedto the atmosphere and maintained under vacuum by said evacuating meansand communicating with said receiver and adapted to receive and collectas a pool stock from the pond overiiowing said weir means, conduit meansfor conveying pooled overiiowed stock from said chamber to the intakeside of said stock-feeding pump means and means regulating the flow ofpooled overflowed ,stock from said 'chamber responsively to the level ofoveriiowed stock pooled in said chamber.

10. Apparatus for providing a constant flow of deaerated aqueouspapermaking stock from a stock deaerating station to a point of use,comprising an enclosed stock receiver adapted to collect deaerated stockas a pond in its lower portion, evacuating means in communication withthe upper portion of said receiver for maintaining the receiver under avacuum sufficient to deaerate papermaking stock subsequently sprayedthereinto, hydrocyclone means adapted to classify aqueous papermakingstock into dirt-rich and dirt-poor fractions and spray the dirt-poorfraction into the upper portion of said receiver, stockeeding pumpvmeansand cooperating conduit means for supplying air-containing aqueouspapermaking stock to said hydrocyclone means, conduit means from saidreceiver and cooperating pump means and` valve means for regulatablyconveying deaerated stock from a pond thereof cggected in the lowerportion of said receiver to said point of use, a chamber closed to theatmosphere and maintained under vacuum sufficient to deaeratepapermaking stock by said evacuating means, Weir means in said receiverpermitting overiiow of deaerated stock from the pond to said chamber,and means for conveying overiowed stock from said chamber to the intakeside of said stock-feeding pump means.

References Cited by the Examiner UNITED STATES PATENTS 18,293 9/57Naughten 210-538 2,487,876 11/49 Johnson 55-169 2,546,259 3/51 McNeil55-204 2,762,451 9/ 5 6 McNeil 5 5-204 2,787,451 4/57 Lavery 55--1662,911,067 11/59 Bludworth et al. 55-38 2,920,763 1/60 Lind et al 210-55X 2,934,141 4/ 60 Ikavalko 162-339 3,095,348 6/63 Goldsmith 55-1913,131,117 4/64 Hickey 55-189 3,163,508 12/64 Tuck et al. 55-204 FOREIGNPATENTS 189,047 2/57 Austria.

85,252 3/58 Denmark. 510,713 10/ 30 Germany.

REUBEN FRIEDMAN, Primary Examiner,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,206,917 September 21, 1965 Robert G. Kaiser et al.

It is hereby certified that error appears in the above numbered patent.requiring correction and that the said Letters Patent should read ascorrected below.

Column 1, line 61, for "deaerated" read --I deaerating column 3, line 7,after "significant" insert change line 44, Jfor "values" read valvescolumn 5, line 68, for "repadly" read rapidly column 6, line 23, for"accesses" read access line 31, for "delivered" read diverted line 44,after "withdrawing" strike out the comma; column 8, line 55, for"2,546,259 3/51 McNei1-55-204" read 2,546,259 3/51 Fenn--55229 I Signedand sealed this 5th day of April 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

3. APPARATUS FOR PROVIDING A CONSTANT FLOW OF DEAERATED AQUEOUSPAPERMAKING STOCK TO A POINT OF USE, COMPRISING AN ENCLOSED STOCKRECEIVER ADAPTED TO COLLECT DEAERATED PAPERMAKING STOCK AS A PONDTHEREIN AND PROVIDE A SPACE ABOVE THE POND, EVACUATING MEANS INCOMMUNICATION WITH THE SPACE ABOVE THE POND IN SAID RECEIVER FORMAINTAINING THE RECEIVER UNDER A VACUUM SUFFICIENT TO DEAERATEPAPERMAKING STOCK SUBSEQUENTLY SPRAYED THEREINTO, MEANS FOR SPRAYINGAIR-CONTAINING AQUEOUS PAPERMAKING STOCK INTO THE EVACUATED SPACE INSAID RECEIVER, MEANS FOR WITHDRAWING DEAERATED STOCK COLLECTED AS A PONDIN SAID RECEIVER AND FOR CONVEYING THE WITHDRAWN